This is a book on the logic of design and hence on how we make, transform, refine, and improve the objects of our knowledge. The starting point is that reality provides the data, to be understood as constraining affordances, and we transform them into information, like semantic engines. Such transformation or repurposing is not equivalent to portraying, or picturing, or photographing, or photocopying anything. It is more like cooking: the dish does not represent the ingredients, it uses them to make something else out of them, yet the reality of the dish and its properties hugely depend on the reality and the properties of the ingredients. Models are not representations understood as pictures, but interpretations understood as data elaborations, of systems. Thus, the whole book may also be read as an articulation and defence of the thesis that knowledge is design, and that philosophy is the ultimate form of conceptual design. This is the third volume in a tetralogy that includes The Philosophy of Information (OUP 2011) and The Ethics of Information (OUP 2013). The three volumes are all written as stand-alone, but they are complementary. By working like a hinge between the two previous books, this third one prepares the basis for volume four, on The Politics of Information. There, the epistemological, conceptual, and normative constructionism supports the study of the design opportunities we have in understanding and shaping what I like to call “the human project” in our information societies.